Abstract: A limiting current type oxygen sensor having a gas diffusion mechanism comprising a gas diffusion bore and an internal space communicating with the gas diffusion bore for supplying a diffusion-rate-determined gas. The gas diffusion mechanism may be configured such that an oxygen concentration gradient within the internal space satisfies the expression: 1/Ilim=(1/4 FDCo2){(l/S)+(lin/Sin)} based on the Faraday constant (F); a diffusion coefficient (D); an oxygen concentration (Co2); a bore area (S) of the gas diffusion bore; a bore length (l) in the axial direction of the gas diffusion bore; a distance (lin) in the internal space between the first electrode and the inner surface opposed thereto; an effective cross section (Sin) of the internal space; and an output current value (Ilim). This makes it possible to accurately sense and measure the oxygen concentration, even at low oxygen concentrations, and achieve easy producibility and cost reducibility.

Abstract: A limiting current type oxygen sensor comprises an ion conductor, a pair of electrodes, a gas diffusion mechanism for supplying a diffusion-rate-determined gas, and a heater for heating the ion conductor. The gas diffusion mechanism includes a gas diffusion bore and an internal space communicating with the gas diffusion bore. In a first embodiment, the gas diffusion mechanism is configured such that the thickness (lin) of the internal space is formed equal to or larger than the bore diameter (S1) of the gas diffusion bore. This makes it possible to dominate diffusion-rate-determinateness in the gas diffusion bore and minimize the influence of diffusion-rate-determinateness in the internal space, thereby sensing the limiting current value accurately. In a second embodiment, the gas diffusion mechanism is configured such that an oxygen concentration gradient within the internal space satisfies the condition of a certain expression.